Triazole derivative, and light-emitting element, light-emitting device, electronic device and lighting device using the triazole derivative

ABSTRACT

Objects are to provide the following: a substance that facilitates hole injection and has high triplet excitation energy; a light-emitting element having high emission efficiency using the substance that facilitates hole injection and has high triplet excitation energy; a light-emitting element having low driving voltage; and a light-emitting device, an electronic device, and a lighting device having low power consumption. Provided is a triazole derivative in which a dibenzothiophen-4-yl or dibenzofuran-4-yl group represented by General Formula (G2) is bonded to any one of Ar 1  to Ar 3  of a triazole derivative represented by General Formula (G1). In the formulas, A represents oxygen or sulfur, Ar 1  to Ar 3  separately represent a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and R 1  to R 7  separately represent hydrogen, an alkyl group having 1 to 4 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms.

This application is a continuation of copending U.S. application Ser.No. 13/110,364, filed on May 18, 2011 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a triazole derivative. Further, thepresent invention relates to a current-excitation light-emitting elementincluding the triazole derivative, and a light-emitting device, anelectronic device and a lighting device each including thelight-emitting element.

2. Description of the Related Art

In recent years, research and development have been extensivelyconducted on light-emitting elements utilizing electroluminescence (EL).In the basic structure of such a light-emitting element, a layercontaining a light-emitting substance is interposed between a pair ofelectrodes. By voltage application to this element, light emission fromthe light-emitting substance can be obtained.

Such light-emitting elements are self-luminous elements and hence haveadvantages over liquid crystal displays in having high pixel visibilityand eliminating the need for backlights, for example; thus,light-emitting elements are suitable for flat panel display elements.Light-emitting elements are also highly advantageous in that they can bethin and lightweight. Furthermore, very high speed response to aninputted signal is one of the features of such elements.

Furthermore, since such light-emitting elements can be formed in a filmform, they make it possible to provide planar light emission. This is adifficult feature to obtain with point light sources typified byincandescent lamps and LEDs or linear light sources typified byfluorescent lamps. Thus, light-emitting elements also have greatpotential as planar light sources applicable to lighting devices and thelike.

Such light-emitting elements utilizing EL can be broadly classifiedaccording to whether a light-emitting substance is an organic compoundor an inorganic compound. In the case of an organic EL element in whicha layer containing an organic compound used as a light-emittingsubstance is provided between a pair of electrodes, application of avoltage to the light-emitting element causes injection of electrons froma cathode and holes from an anode into the layer containing the organiccompound having a light-emitting property and thus a current flows. Theinjected electrons and holes then lead the organic compound having alight-emitting property to its excited state, whereby light emission isobtained from the excited organic compound having a light-emittingproperty.

An excited state formed by an organic compound can be a singlet excitedstate or a triplet excited state. Luminescence from a singlet excitedstate (S*) is called fluorescence, and luminescence from a tripletexcited state (T*) is called phosphorescence. In addition, the ratio ofS* to T* formed in the light-emitting element is statisticallyconsidered to be 1:3.

At room temperature, observations of a compound that can convert energyof a singlet excited state into luminescence (hereinafter, referred toas a fluorescent compound) usually show only luminescence from thesinglet excited state (fluorescence) without luminescence from thetriplet excited state (phosphorescence).

Thus, the internal quantum efficiency (the ratio of generated photons toinjected carriers) of a light-emitting element using a fluorescentcompound is assumed to have a theoretical limit of 25% based on aS*-to-T* ratio of 1:3.

In contrast, with a compound that can convert energy of a tripletexcited state into luminescence (hereinafter, called a phosphorescentcompound), luminescence from the triplet excited state (phosphorescence)is observed. Further, with a phosphorescent compound, since intersystemcrossing (i.e., transition from a singlet excited state to a tripletexcited state) easily occurs, the internal quantum efficiency can beincreased to 75% to 100% in theory. In other words, an element using aphosphorescent compound can have three to four times as high emissionefficiency as that of an element using a fluorescent compound. For thesereasons, a light-emitting element using a phosphorescent compound hasbeen actively developed in recent years in order to achieve ahighly-efficient light-emitting element.

When a light-emitting layer of a light-emitting element is formed usinga phosphorescent compound described above, in order to suppressconcentration quenching or quenching due to triplet-triplet annihilationin the phosphorescent compound, the light-emitting layer is often formedsuch that the phosphorescent compound is dispersed in a matrix ofanother compound. Here, the compound serving as the matrix is called ahost material, and the compound dispersed in the matrix, such as aphosphorescent compound, is called a guest material.

In the case where a phosphorescent compound is a guest material, a hostmaterial needs to have higher triplet excitation energy (an energydifference between a ground state and a triplet excited state) than thephosphorescent compound

Furthermore, since singlet excitation energy (an energy differencebetween a ground state and a singlet excited state) is higher thantriplet excitation energy, a substance that has high triplet excitationenergy also has high singlet excitation energy. Therefore the abovesubstance that has high triplet excitation energy is also effective in alight-emitting element using a fluorescent compound as a light-emittingsubstance.

In Patent Document1,3-(4-biphenylyl)-5-(4-tert-butylphenyl)-4-phenyl-1,2,4-triazole(abbreviation: TAZ) is used as a host material for a phosphorescentcompound that emits green light.

REFERENCE Patent Document

Patent Document 1: Japanese Published Patent Application No. 2002-352957

SUMMARY OF THE INVENTION

A compound having high triplet excitation energy like TAZ is useful as ahost material for a phosphorescent compound. However, TAZ has highsinglet excitation energy and it is also used as a hole-blockingmaterial; that is, a feature of TAZ is that it has great difficulty withhole injection. Thus, when TAZ is used as a host material of alight-emitting layer, holes are difficult to inject into thelight-emitting layer, and accordingly a light-emitting region has astrong tendency to be concentrated in and around an interface betweenthe light-emitting layer and a hole-transport layer. If thelight-emitting region is concentrated in the interface, there occursconcentration quenching of a light-emitting substance in an excitedstate or quenching due to triplet-triplet annihilation, which couldresult in a decrease of emission efficiency.

Therefore, an object of one embodiment of the present invention is toprovide a substance that facilitates hole injection and has high tripletexcitation energy.

Another object of one embodiment of the present invention is to providea light-emitting element having high emission efficiency and low drivingvoltage, which uses the substance that facilitates hole injection andhas high triplet excitation energy. Still another object is to provide alight-emitting device, an electronic device, and a lighting device eachhaving low power consumption.

The present inventors have placed their focus on a triazole derivativewhich includes, in the same molecule, a triazole skeleton having anelectron-transport property and high triplet excitation energy and adibenzothiophene skeleton (or a dibenzofuran skeleton) having ahole-transport property. Then, the inventors have found that thetriazole derivative, in which a triazole skeleton and a dibenzothiopheneskeleton (or a dibenzofuran skeleton) are bonded through an arylenegroup, can be easily synthesized and has high triplet excitation energyand an electron- and hole-transport properties. More specifically, theinventors have found that the triazole derivative is a 1,2,4-triazolederivative, in which an aryl group is bonded to each of the 3-, 4-, and5-positions and a dibenzothiophen-4-yl group or a dibenzofuran-4-ylgroup is bonded to any one of the aryl groups, and the triazolederivative has high triplet excitation energy and an electron- andhole-transport properties.

One embodiment of the present invention is a triazole derivative inwhich a dibenzothiophen-4-yl group or a dibenzofuran-4-yl grouprepresented by General Formula (G2) is bonded to any one of Ar¹ to Ar³of a triazole derivative represented by General Formula (G1).

In General Formulae (G1) and (G2), A represents oxygen or sulfur, Ar¹ toAr³ separately represent a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms, and R¹ to R⁷ separately represent hydrogen,an alkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.

One embodiment of the present invention is a triazole derivativerepresented by General Formula (G3).

In General Formula (G3), A represents oxygen or sulfur, Ar¹ and Ar²separately represent a substituted or unsubstituted aryl group having 6to 13 carbon atoms, Ar⁴ represents a substituted or unsubstitutedarylene group having 6 to 13 carbon atoms, and R¹ to R⁷ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms.

One embodiment of the present invention is a triazole derivativerepresented by General Formula (G4).

In General Formula (G4), A represents oxygen or sulfur, Ar¹ and Ar²separately represent a substituted or unsubstituted aryl group having 6to 13 carbon atoms, and R¹ to R⁷ separately represent hydrogen, an alkylgroup having 1 to 4 carbon atoms, or a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms.

One embodiment of the present invention is a triazole derivativerepresented by General Formula (G5).

In General Formula (G5), A represents oxygen or sulfur, Ar¹ and Ar²separately represent a substituted or unsubstituted aryl group having 6to 13 carbon atoms, and R¹ to R⁷ separately represent hydrogen, an alkylgroup having 1 to 4 carbon atoms, or a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms.

In any of the above triazole derivatives, Ar¹ and Ar² are eachpreferably a phenyl group for easier synthesis.

Another embodiment of the present invention is a light-emitting elementusing any of the above-described triazole derivatives, and specifically,a light-emitting element including any of the above-described triazolederivatives between a pair of electrodes.

Still another embodiment of the present invention is a light-emittingelement which includes a light-emitting layer between a pair ofelectrodes, in which the light-emitting layer has any of the abovetriazole derivatives.

Since the above triazole derivatives have high triplet excitationenergy, a more advantageous effect can be obtained when thelight-emitting layer includes any of the above triazole derivatives anda substance that emits phosphorescence. By using any of the abovetriazole derivatives, highly efficient light emission can be obtainedeven with a substance that emits phosphorescence, especially a substancethat emits short-wavelength light having an emission peak greater thanor equal to 400 nm and less than or equal to 500 nm.

The light-emitting device of one embodiment of the present inventionincludes a light-emitting element having any of the above triazolederivatives and a control circuit which controls light emission of thelight-emitting element. The light-emitting device in this specificationrefers to an image display device and a light source. In addition, thelight-emitting device includes, in its category, all of a module inwhich a connector such as a flexible printed circuit (FPC), a tapeautomated bonding (TAB) tape or a tape carrier package (TCP) isconnected to a panel, a module in which a printed wiring board isprovided on the tip of a TAB tape or a TCP, and a module in which anintegrated circuit (IC) is directly mounted on a light-emitting elementby a chip on glass (COG) method.

The scope of the invention encompasses an electronic device using alight-emitting element of one embodiment of the invention for a displayportion. Thus, an electronic device according to one embodiment of theinvention includes a display portion, in which the display portionincludes any of the above triazole derivatives and a control circuitwhich controls light emission of the light-emitting element.

One embodiment of the present invention can provide a substance thatfacilitates hole injection and has high triplet excitation energy.

By using a triazole derivative of one embodiment of the presentinvention, a light-emitting element having high emission efficiency canbe provided. Further, a light-emitting element having low drivingvoltage can be provided. Furthermore, a light-emitting device, anelectronic device, and a lighting device each having low powerconsumption can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B each illustrate a light-emitting element of anembodiment of the present invention.

FIGS. 2A and 2B each illustrate a light-emitting element of anembodiment of the present invention.

FIGS. 3A and 3B illustrate a light-emitting device according to oneembodiment of the present invention.

FIGS. 4A and 4B illustrate a light-emitting device according to oneembodiment of the present invention.

FIGS. 5A to 5E each illustrate an electronic device according to oneembodiment of the present invention.

FIG. 6 illustrates lighting devices according to one embodiment of thepresent invention.

FIGS. 7A and 7B show the ¹H NMR charts of3-[4-(dibenzothiophen-4-yl)phenyl)]-4,5-diphenyl-4H-1,2,4-triazole(abbreviation: DBTTAZ-II).

FIGS. 8A and 8B show an absorption spectrum and an emission spectrum ofa toluene solution of DBTTAZ-II.

FIGS. 9A and 9B show an absorption spectrum and an emission spectrum ofa thin film of DBTTAZ-II.

FIGS. 10A and 10B each illustrate a light-emitting element of Example.

FIG. 11 shows current density versus luminance characteristics oflight-emitting elements of Example.

FIG. 12 shows voltage versus luminance characteristics of thelight-emitting elements of Example.

FIG. 13 shows luminance characteristics versus current efficiency of thelight-emitting elements of Example.

FIG. 14 shows voltage versus current of the light-emitting elements ofExample.

FIG. 15 shows results of reliability tests of the light-emittingelements of Example.

FIG. 16 shows current density versus luminance characteristics of alight-emitting element of Example.

FIG. 17 shows voltage versus luminance characteristics of thelight-emitting element of Example.

FIG. 18 shows luminance characteristics versus current efficiency of thelight-emitting element of Example.

FIG. 19 shows voltage versus current of the light-emitting element ofExample.

FIGS. 20A and 20B show the ¹H NMR charts of4-[4-(dibenzothiophen-4-yl)phenyl)]-3,5-diphenyl-4H-1,2,4-triazole(abbreviation: 4DBTTAZ-II).

FIGS. 21A and 21B show an absorption spectrum and an emission spectrumof a toluene solution of 4DBTTAZ-II.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. Note that the invention is notlimited to the description given below, and it will be easily understoodby those skilled in the art that various changes and modifications canbe made without departing from the spirit and scope of the invention.Therefore, the invention should not be construed as being limited to thedescription in the following embodiments.

(Embodiment 1)

In Embodiment 1, a triazole derivative of one embodiment of the presentinvention will be described.

A triazole derivative of one embodiment of the present inventionincludes, in the same molecule, a triazole skeleton having anelectron-transport property and high triplet excitation energy and adibenzothiophene skeleton (or a dibenzofuran skeleton) having ahole-transport property. Specifically, the triazole derivative is a1,2,4-triazole derivative in which an aryl group is bonded to each ofthe 3-, 4-, and 5-positions and a dibenzothiophen-4-yl group or adibenzofuran-4-yl group is bonded to any one of the aryl groups.

One embodiment of the present invention is a triazole derivative inwhich a dibenzothiophen-4-yl group or a dibenzofuran-4-yl grouprepresented by General Formula (G2) is bonded to any one of Ar¹ to Ar³of a triazole derivative represented by General Formula (G1).

In General Formulae (G1) and (G2), A represents oxygen or sulfur, Ar¹ toAr³ separately represent a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms, and R¹ to R⁷ separately represent hydrogen,an alkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.

An example of the above triazole derivative is a triazole derivativerepresented by General Formula (G3).

In General Formula (G3), A represents oxygen or sulfur, Ar¹ and Ar²separately represent a substituted or unsubstituted aryl group having 6to 13 carbon atoms, Ar⁴ represents a substituted or unsubstitutedarylene group having 6 to 13 carbon atoms, and R¹ to R⁷ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms.

As a triazole derivative of one embodiment of the present invention, atriazole derivative represented by General Formula (G4) is preferred foreasier synthesis, and a triazole derivative represented by GeneralFormula (G5) is more preferred for easier synthesis due to its reducedsteric hindrance.

In General Formulae (G4) and (G5), A represents oxygen or sulfur, Ar¹and Ar² separately represent a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms, and R¹ to R⁷ separately represent hydrogen,an alkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.

Examples of the specific structures of Ar¹ to Ar³ in a triazolederivative of one embodiment of the present invention includesubstituents represented by Structural Formulae (1-1) to (1-14).

Examples of the specific structures of Ar⁴ in a triazole derivative ofone embodiment of the present invention include substituents representedby Structural Formulae (2-1) to (2-15).

Examples of the specific structures of R¹ to R⁷ in a triazole derivativeof one embodiment of the present invention include substituentsrepresented by Structural Formulae (3-1) to (3-23).

In a triazole derivative of one embodiment of the present invention, Ar¹and Ar² are each preferably a phenyl group for easier synthesis.Furthermore, Ar¹ and Ar² are each preferably a phenyl group also inorder to obtain high triplet excitation energy.

Specific examples of a triazole derivative of one embodiment of thepresent invention include, but are not limited to, triazole derivativesrepresented by Structural Formulae (100) to (167) and (200) to (267).

A variety of reactions can be applied to a method of synthesizing atriazole derivative of one embodiment of the present invention. Forexample, synthesis reactions described below enable the synthesis of atriazole derivative of one embodiment of the present invention. Now,description of methods of synthesizing compounds (G6) and (G7) to beproduced is shown below, which are examples of the triazole derivativeof one embodiment of the present invention. Note that the methods ofsynthesizing the triazole derivatives of one embodiment of the presentinvention are not limited to the synthesis methods described below.

[Method of Synthesizing Triazole Derivative Represented by GeneralFormula (G6)]

First, Synthesis Scheme (A-1) will be illustrated below.

The triazole derivative (G6) of one embodiment of the present inventioncan be synthesized as illustrated in Synthesis Scheme (A-1).Specifically, a halide of a 4H-triazole derivative or a triazolederivative that has a triflate group as a substituent (Compound 1) iscoupled with an organoboron compound or boronic acid of a dibenzofuranderivative or a dibenzothiophene derivative (Compound 2) by aSuzuki-Miyaura reaction, whereby the compound (G6) to be produced can beobtained.

In Synthesis Scheme (A-1), A represents oxygen or sulfur, and R¹ to R⁷separately represent hydrogen, an alkyl group having 1 to 4 carbonatoms, or a substituted or unsubstituted aryl group having 6 to 13carbon atoms. Further, R⁵⁰ and R⁵¹ separately represent hydrogen or analkyl group having 1 to 6 carbon atoms, Ar¹ and Ar² separately representa substituted or unsubstituted aryl group having 6 to 13 carbon atoms,and Ar³ represents a substituted or unsubstituted arylene group having 6to 13 carbon atoms. In Synthesis Scheme (A-1), R⁵⁰ and R⁵¹ may be bondedto each other to form a ring. Furthermore, X¹ represents a halogen or atriflate.

Examples of the palladium catalyst that can be used in Synthesis Scheme(A-1) include, but are not limited to, palladium(II) acetate,tetrakis(triphenylphosphine)palladium(0),bis(triphenylphosphine)palladium(II) dichloride, and the like. Examplesof the ligand of the palladium catalyst which can be used in SynthesisScheme (A-1) include, but are not limited to, tri(ortho-tolyl)phosphine,triphenylphosphine, tricyclohexylphosphine, and the like.

Examples of the base that can be used in Synthesis Scheme (A-1) include,but are not limited to, organic bases such as sodium tert-butoxide,inorganic bases such as potassium carbonate and sodium carbonate, andthe like.

Examples of the solvent that can be used in Synthesis Scheme (A-1)include, but are not limited to, a mixed solvent of toluene and water; amixed solvent of toluene, alcohol such as ethanol, and water; a mixedsolvent of xylene and water; a mixed solvent of xylene, alcohol such asethanol, and water; a mixed solvent of benzene and water; a mixedsolvent of benzene, alcohol such as ethanol, and water; a mixed solventof water and an ether such as ethylene glycol dimethyl ether; and thelike. It is more preferable to use a mixed solvent of toluene and water,a mixed solvent of toluene, ethanol, and water, or a mixed solvent ofwater and an ether such as ethylene glycol dimethyl ether.

As a coupling reaction illustrated in Synthesis Scheme (A-1), theSuzuki-Miyaura reaction using the organoboron compound or the boronicacid represented by Compound 2 may be replaced with a cross couplingreaction using an organoaluminum compound, an organozirconium compound,an organozinc compound, an organotin compound, or the like. However, thepresent invention is not limited thereto.

Further, in the Suzuki-Miyaura Coupling Reaction illustrated inSynthesis Scheme (A-1), an organoboron compound or boronic acid of a4H-triazole derivative may be coupled with a halide of a dibenzofuranderivative, or a dibenzothiophene derivative or with a carbazolederivative, a dibenzofuran derivative, or a dibenzothiophene derivativewhich has a triflate group as a substituent, by the Suzuki-Miyaurareaction.

In the above manner, the triazole derivative of this embodiment can besynthesized.

[Method of Synthesizing Triazole Derivative Represented by GeneralFormula (G7)]

First, Synthesis Scheme (B-1) will be illustrated below.

As illustrated in Synthesis Scheme (B-1), a halide of a 4H-triazolederivative or a triazole derivative that has a triflate group as asubstituent (Compound 3) is coupled with an organoboron compound orboronic acid of a dibenzofuran derivative or a dibenzothiophenederivative (Compound 4) by a Suzuki-Miyaura reaction, whereby thecompound (G7) to be produced can be obtained.

In Synthesis Scheme (B-1), A represents oxygen or sulfur, and R¹ to R⁷separately represent hydrogen, an alkyl group having 1 to 4 carbonatoms, or a substituted or unsubstituted aryl group having 6 to 13carbon atoms. Further, R⁵² and R⁵³ separately represent hydrogen or analkyl group having 1 to 6 carbon atoms, Ar¹ and Ar³ separately representa substituted or unsubstituted aryl group having 6 to 13 carbon atoms,and Ar² represents a substituted or unsubstituted arylene group having 6to 13 carbon atoms. In Synthesis Scheme (B-1), R⁵² and R⁵³ may be bondedto each other to form a ring. Furthermore, X² represents a halogen or atriflate.

Examples of the palladium catalyst that can be used in Synthesis Scheme(B-1) include, but are not limited to, palladium(II) acetate,tetrakis(triphenylphosphine)palladium(0),bis(triphenylphosphine)palladium(II) dichloride, and the like. Examplesof the ligand of the palladium catalyst which can be used in SynthesisScheme (B-1) include, but are not limited to, tri(ortho-tolyl)phosphine,triphenylphosphine, tricyclohexylphosphine, and the like.

Examples of the base that can be used in Synthesis Scheme (B-1) include,but are not limited to, organic bases such as sodium tert-butoxide,inorganic bases such as potassium carbonate and sodium carbonate, andthe like.

Examples of the solvent that can be used in Synthesis Scheme (B-1)include, but are not limited to, a mixed solvent of toluene and water; amixed solvent of toluene, alcohol such as ethanol, and water; a mixedsolvent of xylene and water; a mixed solvent of xylene, alcohol such asethanol, and water; a mixed solvent of benzene and water; a mixedsolvent of benzene, alcohol such as ethanol, and water; a mixed solventof water and an ether such as ethylene glycol dimethyl ether; and thelike. It is more preferable to use a mixed solvent of toluene and water,a mixed solvent of toluene, ethanol, and water, or a mixed solvent ofwater and an ether such as ethylene glycol dimethyl ether.

As a coupling reaction illustrated in Synthesis Scheme (B-1), theSuzuki-Miyaura reaction using the organoboron compound or the boronicacid represented by Compound 4 may be replaced with a cross couplingreaction using an organoaluminum compound, an organozirconium compound,an organozinc compound, an organotin compound, or the like. However, thepresent invention is not limited thereto.

Further, in the Suzuki-Miyaura Coupling Reaction illustrated inSynthesis Scheme (B-1), an organoboron compound or boronic acid of a4H-triazole derivative may be coupled with a halide of a dibenzofuranderivative, or a dibenzothiophene derivative or with a carbazolederivative, a dibenzofuran derivative, or a dibenzothiophene derivativewhich has a triflate group as a substituent, by the Suzuki-Miyaurareaction.

By the above-described method, the triazole derivative of thisembodiment can be synthesized.

A triazole derivative of this embodiment has high triplet excitationenergy and an electron- and hole-transport properties, and therefore thetriazole derivative can be suitably used for a light-emitting element.Because the balance between injected electrons and holes is important ina light-emitting layer of a light-emitting element, a triazolederivative of one embodiment of the present invention is preferably usedfor a light-emitting layer, in particular. Further, owing to the hightriplet excitation energy, a triazole derivative of one embodiment ofthe present invention can be used for a light-emitting layer incombination with a substance that emits phosphorescence. Even when usedfor a light-emitting layer in combination with a substance that emitsphosphorescence, especially a substance that emits short-wavelengthlight having an emission peak greater than or equal to 400 nm and lessthan or equal to 500 nm, a triazole derivative of one embodiment of thepresent invention is capable of realizing high emission efficiency.

Furthermore, since singlet excitation energy (an energy differencebetween a ground state and a singlet excited state) is higher thantriplet excitation energy, a substance that has high triplet excitationenergy also has high singlet excitation energy. Therefore, a triazolederivative of one embodiment of the present invention, which has hightriplet excitation energy, is effective also when used for alight-emitting layer in combination with a substance that emitsfluorescence.

Further, a triazole derivative of one embodiment of the presentinvention can be used for a carrier-transport layer in a light-emittingelement since the triazole derivative can transport carrier. Owing tothe high triplet energy, a triazole derivative of one embodiment of thepresent invention does not easily allow energy transfer from alight-emitting layer and can realize high emission efficiency even whenthe triazole derivative is used for a layer in contact with thelight-emitting layer.

(Embodiment 2)

In Embodiment 2, as one embodiment of the present invention, alight-emitting element in which a triazole derivative is used for an ELlayer will be described with reference to FIGS. 1A and 1B.

In a light-emitting element of this embodiment, the EL layer having atleast a light-emitting layer is interposed between a pair of electrodes.The EL layer may also have a plurality of layers in addition to thelight-emitting layer. The plurality of layers is a combination of alayer containing a substance having a high carrier-injection propertyand a layer containing a substance having a high carrier-transportproperty which are stacked so that a light-emitting region is formed ina region away from the electrodes, that is, so that carriers recombinein a region away from the electrodes. In this specification, the layercontaining a substance having a high carrier-injection or-transportproperty is also referred to as a functional layer which functions toinject or transport carriers, for example. As a functional layer, ahole-injection layer, a hole-transport layer, an electron-injectionlayer, an electron-transport layer, or the like can be used.

In the light-emitting element of this embodiment illustrated in FIG. 1A,an EL layer 102 having a light-emitting layer 113 is provided between apair of electrodes, a first electrode 101 and a second electrode 103.The EL layer 102 includes a hole-injection layer 111, a hole-transportlayer 112, the light-emitting layer 113, an electron-transport layer114, and an electron-injection layer 115. The light-emitting element inFIG. 1A includes the first electrode 101 formed over a substrate 100,the hole-injection layer 111, the hole-transport layer 112, thelight-emitting layer 113, the electron-transport layer 114, and theelectron-injection layer 115 which are stacked over the first electrode101 in this order, and the second electrode 103 provided thereover. Notethat, in the light-emitting element described in this embodiment, thefirst electrode 101 functions as an anode and the second electrode 103functions as a cathode.

The substrate 100 is used as a support of the light-emitting element.For example, glass, quartz, plastic, or the like can be used for thesubstrate 100. A flexible substrate may also be used. The flexiblesubstrate is a substrate that can be bent, such as a plastic substratemade of polycarbonate, polyarylate, or polyether sulfone, for example. Afilm (made of polypropylene, polyester, vinyl, polyvinyl fluoride, vinylchloride, or the like), an inorganic film formed by evaporation, or thelike can also be used. Note that materials other than these can be usedas long as they can function as a support of the light-emitting element.

For the first electrode 101, any of metals, alloys, electricallyconductive compounds, mixtures thereof, and the like which has a highwork function (specifically, a work function of 4.0 eV or more) ispreferably used. Specific examples include indium oxide-tin oxide (ITO:indium tin oxide), indium oxide-tin oxide containing silicon or siliconoxide, indium oxide-zinc oxide (IZO: indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide (IWZO), and the like. Films ofthese conductive metal oxides are usually formed by sputtering; however,a sol-gel method or the like may also be applied. For example, an IZOfilm can be formed by a sputtering method using a target obtained byadding 1 wt % to 20 wt % of zinc oxide to indium oxide. An IWZO film canbe formed by a sputtering method using a target obtained by adding 0.5wt % to 5 wt % of tungsten oxide and 0.1 wt % to 1 wt % of zinc oxide toindium oxide. Other examples for materials of the first electrode 101are gold, platinum, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, palladium, nitrides of metal materials (e.g., titaniumnitride), and the like.

When a layer included in the EL layer 102 which is formed in contactwith the first electrode 101 is formed using a later described compositematerial in which an organic compound and an electron acceptor(acceptor) are mixed, the first electrode 101 can be formed using any ofvarious types of metals, alloys, and electrically-conductive compounds,a mixture thereof, and the like regardless of the work function. Forexample, aluminum, silver, an alloy containing aluminum (e.g., Al—Si),or the like can be used.

The EL layer 102 formed over the first electrode 101 has at least thelight-emitting layer 113 and includes a triazole derivative which is oneembodiment of the present invention. The EL layer 102 can also include aknown substance as a part, which can be either a low molecular compoundor a high molecular compound. Note that substances forming the EL layer102 may consist of organic compounds or may include an inorganiccompound as a part.

As illustrated in FIGS. 1A and 1B, the EL layer 102 is formed bystacking as appropriate the hole-injection layer 111, the hole-transportlayer 112, the electron-transport layer 114, the electron-injectionlayer 115, and the like in combination in addition to the light-emittinglayer 113.

The hole-injection layer 111 is a layer containing a substance having ahigh hole-injection property. Examples of applicable substances having ahigh hole-injection property are metal oxides such as molybdenum oxide,titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromiumoxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide,tungsten oxide, and manganese oxide. Other examples of applicablesubstances are phthalocyanine-based compounds such as phthalocyanine(abbreviation: H₂Pc) and copper(II) phthalocyanine (abbreviation: CuPc).

Other examples of applicable substances are aromatic amine compoundswhich are low molecular organic compounds such as4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1).

Still other examples of applicable substances are high molecularcompounds (e.g., oligomers, dendrimers, and polymers) such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine)(abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD), and high molecular compounds to which acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS),or polyaniline/poly(styrenesulfonic acid) (PAni/PSS).

For the hole-injection layer 111, the composite material in which anorganic compound and an electron acceptor (acceptor) are mixed may beused. Such a composite material, in which holes are generated in theorganic compound by the electron acceptor, has excellent hole injectionand transport properties. The organic compound here is preferably amaterial excellent in transporting the generated holes (a substancehaving a high hole-transport property).

Examples of the organic compound used for the composite material are avariety of compounds such as aromatic amine compounds, carbazolederivatives, aromatic hydrocarbons, and high molecular compounds (e.g.,oligomers, dendrimers, and polymers), and preferably organic compoundshaving a high hole-transport property, and specifically preferablysubstances having a hole mobility of 10⁻⁶ cm²/Vs or more. Note thatother than these substances, any substance that has a property oftransporting more holes than electrons may be used. The organiccompounds which can be used for the composite material will bespecifically described below.

Examples of the organic compound that can be used for the compositematerial are aromatic amine compounds such as TDATA, MTDATA, DPAB,DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP),and carbazole derivatives such as 4,4′-di(N-carbazolyl)biphenyl(abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene(abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),9-phenyl-3-[4-(10-phenyl-9-anthryflphenyl]-9H-carbazole (abbreviation:PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl-2,3,5,6-tetraphenylbenzene.

Other examples of the organic compound that can be used are aromatichydrocarbon compounds such as 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),9,10-bis[2-(1-naphthyl)phenyl]-2-tert-butylanthracene, and9,10-bis[2-(1-naphthyl)phenyl]anthracene.

Other examples of the organic compound that can be used are aromatichydrocarbon compounds such as2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene,pentacene, coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi), and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene(abbreviation: DPVPA).

Further, examples of the electron acceptor are organic compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) and chloranil, transition metal oxides, and oxides of metalsthat belong to Groups 4 to 8 in the periodic table. Specific preferredexamples include vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide because their electron-acceptor properties are high. Among these,molybdenum oxide is especially preferable since it is stable in the airand its hygroscopic property is low and is easily treated.

The composite material may be formed using the above-described electronacceptor and the above-described high molecular compound such as PVK,PVTPA, PTPDMA, or Poly-TPD and used for the hole-injection layer 111.

The hole-transport layer 112 is a layer that contains a substance havinga high hole-transport property. Examples of the substance having a highhole-transport property are aromatic amine compounds such as NPB, TPD,BPAFLP, 4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The substances mentioned here are mainlysubstances that have a hole mobility of 10⁻⁶ cm²/Vs or more. Note thatother than the above substances, any substance that has a property oftransporting more holes than electrons may be used. Further, the layerincluding a substance having a high hole-transport property is notlimited to a single layer, and may be a stack of two or more layerscontaining any of the above substances.

For the hole-transport layer 112, a carbazole derivative such as CBP,CzPA, or PCzPA or an anthracene derivative such as t-BuDNA, DNA, orDPAnth may be used.

For the hole-transport layer 112, a high molecular compound such as PVK,PVTPA, PTPDMA, or Poly-TPD can be used.

The light-emitting layer 113 is a layer including a light-emittingsubstance. Note that in Embodiment 2, the case where a triazolederivative of one embodiment of the present invention described inEmbodiment 1 is used for the light-emitting layer is described. Atriazole derivative of one embodiment of the present invention has hightriplet excitation energy and high singlet excitation energy. Therefore,for the light-emitting layer in which a light-emitting substance (aguest material) is dispersed in another substance (a host material), atriazole derivative of one embodiment of the present invention isparticularly preferably used as the host material. By using a triazolederivative of one embodiment of the present invention, thelight-emitting layer 113 can be a light-emitting layer having a highelectron-transport property. By dispersing the guest material which is alight-emitting substance in a triazole derivative of one embodiment ofthe present invention, light emission from the guest material can beobtained.

In addition, more than one kind of substances can be used as thesubstances (host materials) in which the light-emitting substance (guestmaterial) is dispersed. The light-emitting layer may thus include asecond host material in addition to a triazole derivative of oneembodiment of the present invention.

As the light-emitting substance, for example, a fluorescent compound,which emits fluorescence, or a phosphorescent compound, which emitsphosphorescence, can be used.

In the case of the use of a fluorescent compound, a substance havinglower singlet excitation energy than a triazole derivative of oneembodiment of the present invention is preferably used. Since a triazolederivative of one embodiment of the present invention has high singletexcitation energy, the fluorescent compound used for the light-emittinglayer 113 can be selected from a wide range of materials.

The fluorescent compounds that can be used for the light-emitting layer113 will be given. Examples of the materials that emits blue lightincludeN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA), and the like. In addition, examples of thematerials that emits green light includeN-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),N-[9,10-bis(1,1′-biphenyl-2-yl)]-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), and the like. Further, examples of thematerials that emits yellow light include rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),and the like. Furthermore, examples of the materials that emits redlight include N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine(abbreviation: p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD), and the like.

In the case of the use of a phosphorescent compound, a substance havinglower triplet excitation energy than a triazole derivative described inEmbodiment 1 is preferably used. Since a triazole derivative describedin Embodiment 1 has high triplet excitation energy, the phosphorescentcompound used for the light-emitting layer 113 can be selected from awide range of materials. Even when used for the light-emitting layer 113in combination with a phosphorescent compound that emitsshort-wavelength light having an emission peak greater than or equal to400 nm and less than or equal to 500 nm (blue light), in particular, atriazole derivative described in Embodiment 1 is capable of realizinghigh emission efficiency.

The phosphorescent compounds that can be used for the light-emittinglayer 113 will be given. Examples of the materials that emits blue lightincludebis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate(abbreviation: FIr6),bis[2-(4,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate(abbreviation: Ir(CF₃ppy)₂(pic)),bis[2-(4,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate(abbreviation: FIr(acac)), and the like. Examples of the materials thatemits green light include tris(2-phenylpyridinato-N,C^(2′))iridium(III)(abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(ppy)₂(acac)),bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate(abbreviation: Ir(pbi)₂(acac)),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation:Ir(bzq)₂(acac)), tris(benzo[h]quinolinato)iridium(III) (abbreviation:Ir(bzq)₃), and the like. Examples of the materials that emits yellowlight includebis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis[2-(4′-(perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(bt)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)-5-methylpyrazinato]iridium(III)(abbreviation: Ir(Fdppr-Me)₂(acac)),(acetylacetonato)bis{2-(4-methoxyphenyl)-3,5-dimethylpyrazinato}iridium(III)(abbreviation: Ir(dmmoppr)₂(acac)), and the like. Examples of thematerials that emits orange light includetris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation: Ir(pq)₃),bis(2-phenylquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(pq)₂(acac)),(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)),(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)), and the like. Examples of thematerials that emits red light include organometallic complexes such asbis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′))iridium(III)acetylacetonate(abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),(dipivaloylmethanato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(dpm)), and(2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine)platinum(II)(abbreviation: PtOEP). Any of the following rare-earth metal complexescan be used as a phosphorescent compound:tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:[Tb(acac)₃(Phen));tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: [Eu(DBM)₃(Phen)); andtris[1-(2-thenyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: [Eu(TTA)₃(Phen)), because their lightemission is from a rare-earth metal ion (electronic transition betweendifferent multiplicities) in such a rare-earth metal complex.

As the light-emitting substance, a high molecular compound can be used.Specifically, examples of the materials that emits blue light includepoly(9,9-dioctylfluorene-2,7-diyl) (abbreviation: PFO),poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,5-dimethoxybenzene-1,4-diyl)](abbreviation: PF-DMOP),poly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N′-di-(p-butylphenyl)-1,4-diaminobenzene]}(abbreviation: TAB-PFH), and the like. Further, examples of thematerials that emits green light include poly(p-phenylenevinylene)(abbreviation: PPV),poly[(9,9-dihexylfluorene-2,7-diyl)-alt-co-(benzo[2,1,3]thiadiazole-4,7-diyl)](abbreviation: PFBT),poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)],and the like. Furthermore, examples of the materials that emits orangeto red light includepoly[2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylenevinylene] (abbreviation:MEH-PPV), poly(3-butylthiophene-2,5-diyl) (abbreviation: R4-PAT),poly{[9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene]-ah-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]},poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-bis(1-cyanovinylenephenylene)]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}(abbreviation: CN-PPV-DPD), and the like

The electron-transport layer 114 is a layer including a substance havinga high electron-transport property. A triazole derivative of oneembodiment of the present invention described in Embodiment 1 can besuitably used for the electron-transport layer 114, since the triazolederivative has an excellent electron-transport property. When a triazolederivative of one embodiment of the present invention is used for theelectron-transport layer 114, the host material of the light-emittinglayer is not limited to a triazole derivative of one embodiment of thepresent invention and may be any other material.

As the substance having a high electron-transport property, thefollowing metal complexes having a quinoline skeleton or abenzoquinoline skeleton can be given: tris(8-quinolinolato)aluminum(abbreviation: Alq); tris(4-methyl-8-quinolinolato)aluminum(abbreviation: Almq₃); bis(10-hydroxybenzo[h]-quinolinato)beryllium(abbreviation: BeBq₂); andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). A metal complex having an oxazole-based or thiazole-based ligand,such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation:Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂), or the like can also be used. Other than metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can be used. Thesubstances described here are mainly materials having an electronmobility of 10⁻⁶ cm²/Vs or more. Further, the electron-transport layeris not limited to a single layer, and may be a stack of two or morelayers containing any of the above substances are stacked.

The electron-injection layer 115 is a layer that contains a substancehaving a high electron-injection property. Examples of the substancethat can be used for the electron-injection layer 115 are alkali metals,alkaline earth-metals, and compounds thereof, such as lithium, cesium,calcium, lithium fluoride, cesium fluoride, calcium fluoride, andlithium oxide, rare earth-metal compounds such as erbium fluoride, andthe above-mentioned substances for forming the electron-transport layer114.

Alternatively, a composite material in which an organic compound and anelectron donor (donor) are mixed may be used for the electron-injectionlayer 115. Such a composite material, in which electrons are generatedin the organic compound by the electron donor, has excellent electroninjection and transport properties. The organic compound here ispreferably a material excellent in transporting the generated electrons,as which specifically any of the above substances (such as metalcomplexes and heteroaromatic compounds) for the electron-transport layer114 can be used. The electron donor can be a substance exhibiting anelectron-donating property for the organic compound. Specific examplesof the electron donor are alkali metals, alkaline-earth-metals, and rareearth-metals, such as lithium, cesium, magnesium, calcium, erbium, andytterbium. Any of alkali metal oxides and alkaline-earth-metal oxides ispreferable, examples of which are lithium oxide, calcium oxide, bariumoxide, and the like, and a Lewis base such as magnesium oxide or anorganic compound such as tetrathiafulvalene (abbreviation: TTF) can beused.

Note that the hole-injection layer 111, the hole-transport layer 112,the light-emitting layer 113, the electron-transport layer 114, and theelectron-injection layer 115 which are described above can each beformed by a method such as an evaporation method (e.g., a vacuumevaporation method), an inkjet method, or a coating method.

When the second electrode 103 functions as a cathode, any of metals,alloys, electrically conductive compounds, mixtures thereof, and thelike which has a low work function (specifically, a work function of 3.8eV or less) is preferably used for the second electrode 103. Specificexamples of the substance that can be used are elements that belong toGroups 1 and 2 in the periodic table, that is, alkali metals such aslithium and cesium, alkaline earth-metals such as magnesium, calcium,and strontium, alloys thereof (e.g., Mg—Ag and Al—Li), rare earth-metalssuch as europium and ytterbium, alloys thereof, aluminum, silver, andthe like.

When a layer included in the EL layer 102 which is formed in contactwith the second electrode 103 is formed using the composite material inwhich the organic compound and the electron donor (donor), which aredescribed above, are mixed, a variety of conductive materials such asaluminum, silver, ITO, and indium oxide-tin oxide containing silicon orsilicon oxide can be used regardless of the work function.

Note that the second electrode 103 can be formed by a vacuum evaporationmethod or a sputtering method. In the case of using a silver paste orthe like, a coating method, an inkjet method, or the like can be used.

In the above-described light-emitting element, a current flows due to apotential difference generated between the first electrode 101 and thesecond electrode 103 and holes and electrons recombine in the EL layer102, whereby light is emitted. Then, this emitted light is extractedoutside through one or both of the first electrode 101 and the secondelectrode 103. Therefore, one or both of the first electrode 101 and thesecond electrode 103 are electrodes having a property of transmittingvisible light.

Further, the structure of the layers provided between the firstelectrode 101 and the second electrode 103 is not limited to the abovedescribed structure. A structure other than the above may alternativelybe employed as long as a light-emitting region in which holes andelectrons recombine is provided in a portion away from the firstelectrode 101 and the second electrode 103 in order to prevent quenchingdue to proximity of the light-emitting region to metal.

In other words, there is no particular limitation on a stack structureof the layers. A layer including a substance having a highelectron-transport property, a substance having a high hole-transportproperty, a substance having a high electron-injection property, asubstance having a high hole-injection property, a bipolar substance (asubstance having a high electron-transport property and a highhole-transport property), a hole-blocking material, or the like mayfreely be combined with a light-emitting layer including a triazolederivative of one embodiment of the present invention described inEmbodiment 1 as a host material.

In the light-emitting element illustrated in FIG. 1B, the EL layer 102is provided between the first electrode 101 and the second electrode 103over the substrate 100. The EL layer 102 includes the hole-injectionlayer 111, the hole-transport layer 112, the light-emitting layer 113,the electron-transport layer 114, and the electron-injection layer 115.The light-emitting element in FIG. 1B includes the second electrode 103serving as a cathode over the substrate 100, the electron-injectionlayer 115, the electron-transport layer 114, the light-emitting layer113, the hole-transport layer 112, and the hole-injection layer 111which are stacked over the second electrode 103 in this order, and thefirst electrode 101 provided thereover which serves as an anode.

A method of forming the light-emitting element will now be specificallydescribed.

In a light-emitting element of this embodiment, the EL layer isinterposed between the pair of electrodes. The EL layer has at least thelight-emitting layer, and the light-emitting layer is formed using atriazole derivative of one embodiment of the present invention describedin Embodiment 1 as a host material. Further, the EL layer may include afunctional layer (e.g., the hole-injection layer, the hole-transportlayer, the electron-transport layer, or the electron-injection layer) inaddition to the light-emitting layer. The electrodes (the firstelectrode and the second electrode), the light-emitting layer, and thefunctional layer may be formed by any of the wet processes such as adroplet discharging method (an inkjet method), a spin coating method,and a printing method, or by a dry processes such as a vacuumevaporation method, a CVD method, and a sputtering method. A wet processallows formation at atmospheric pressure with a simple device and by asimple process, which gives the effects of simplifying the process andimproving productivity. In contrast, a dry process does not needdissolution of a material and enables use of a material that has lowsolubility in a solution, which expands the range of material choices.

All the thin films included in a light-emitting element may be formed bya wet method. In this case, the light-emitting element can bemanufactured with only facilities needed for a wet process.Alternatively, the following method may be employed: formation of thestacked layers up to formation of the light-emitting layer is performedby a wet process whereas the functional layer, the first electrode, andthe like which are stacked over the light-emitting layer are formed by adry process. Further alternatively, the following method may beemployed: the second electrode and the functional layer are formed by adry process before the formation of the light-emitting layer whereas thelight-emitting layer, the functional layer stacked thereover, and thefirst electrode are formed by a wet process. Needless to say, thisembodiment is not limited to these, and a light-emitting element can beformed by appropriate selection from a wet method and a dry methoddepending on a material to be used, necessary film thickness, and theinterface state.

In this embodiment, a light-emitting element is fabricated over asubstrate made of glass, plastic or the like. By forming a plurality ofsuch light-emitting elements over one substrate, a passive matrixlight-emitting device can be manufactured. Further, a light-emittingelement may be fabricated in such a manner that a thin film transistor(TFT), for example, is be formed over a substrate made of glass,plastic, or the like and the element is formed over an electrodeelectrically connected to the TFT. Thus, an active matrix light-emittingdevice in which the TFT controls the driving of the light-emittingelement can be manufactured. Note that there is no particular limitationon the structure of the TFT: a staggered TFT or an inverted staggeredTFT may be employed. In addition, there is no particular limitation onthe crystallinity of a semiconductor used for the TFT, and an amorphoussemiconductor or a crystalline semiconductor may be used. Furthermore, adriver circuit formed over a TFT substrate may be formed with bothn-channel TFTs and p-channel TFTs or may be formed with either n-channelTFTs or p-channel TFTs.

A triazole derivative of one embodiment of the present inventiondescribed in Embodiment 1 has high triplet excitation energy and anelectron- and hole-transport properties. Therefore, by using a triazolederivative of one embodiment of the present invention described inEmbodiment 1, a light-emitting element having high emission efficiencyand/or low driving voltage can be obtained.

Furthermore, a light-emitting device (such as an image display device)using a light-emitting element of one embodiment of the presentinvention which is obtained as above can have reduced power consumption.

By use of the light-emitting element described in this embodiment, apassive matrix light-emitting device or an active matrix light-emittingdevice in which driving of the light-emitting element is controlled by athin film transistor (TFT) can be manufactured.

This embodiment can be used in appropriate combination with any of theother embodiments.

(Embodiment 3)

In this embodiment, modes of light-emitting elements having a structurein which a plurality of light-emitting units is stacked (hereinafter,referred to as a stacked-type element) will be described with referenceto FIGS. 2A and 2B. These light-emitting element are each alight-emitting element including a plurality of light-emitting unitsbetween a first electrode and a second electrode.

In FIG. 2A, a first light-emitting unit 311 and a second light-emittingunit 312 are stacked between a first electrode 301 and a secondelectrode 303. In this embodiment, the first electrode 301 functions asan anode and the second electrode 303 functions as a cathode. The firstelectrode 301 and the second electrode 303 can be the same as those inEmbodiment 2. Further, the first light-emitting unit 311 and the secondlight-emitting unit 312 may have the same or different structures. Thefirst light-emitting unit 311 and the second light-emitting unit 312 mayhave the same structure as the EL layer of Embodiment 2, or either ofthe units may differ in structure from the EL layer.

Further, a charge generation layer 313 is provided between the firstlight-emitting unit 311 and the second light-emitting unit 312. Thecharge generation layer 313 has a function of injecting electrons intoone of the light-emitting units and injecting holes into the other ofthe light-emitting units when a voltage is applied to the firstelectrode 301 and the second electrode 303. In the case of thisembodiment, when a voltage is applied so that the potential of the firstelectrode 301 is higher than that of the second electrode 303, thecharge generation layer 313 injects electrons into the firstlight-emitting unit 311 and injects holes into the second light-emittingunit 312.

Note that the charge generation layer 313 preferably has a property oftransmitting visible light in terms of light extraction efficiency.Further, the charge generation layer 313 functions even if it has lowerconductivity than the first electrode 301 or the second electrode 303.

The charge generation layer 313 may have a structure in which itincludes the organic compound having a high hole-transport property andthe electron acceptor (acceptor) or a structure in which it includes anorganic compound having a high electron-transport property and theelectron donor (donor), or may be a stack of both of these structures.

In the case of the structure in which the organic compound having a highhole-transport property and the electron acceptor are included, examplesof the substance that can be used as the organic compound having a highhole-transport property are aromatic amine compounds such as NPB, TPD,TDATA, MTDATA, and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), and the like. The substances mentioned here aremainly substances that have a hole mobility of 10⁻⁶ cm²/Vs or more. Notethat other than the above substances, any substance that has a propertyof transporting more holes than electrons may be used.

Examples of the electron acceptor are7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, oxides of transition metals, and oxides of metalsthat belong to Groups 4 to 8 in the periodic table, and the like.Specific preferred examples include vanadium oxide, niobium oxide,tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,manganese oxide, and rhenium oxide because their electron-acceptorproperties are high. Among these, molybdenum oxide is especiallypreferable since it is stable in the air and its hygroscopic property islow and is easily treated.

In the case of the structure in which the organic compound having a highelectron-transport property and the electron donor are included,examples of the organic compound having a high electron-transportproperty which can be used are: metal complexes having a quinolineskeleton or a benzoquinoline skeleton such as Alq, Almq₃, BeBq₂, andBAlq; metal complexes having an oxazole-based ligand or a thiazole-basedligand, such as Zn(BOX)₂ and Zn(BTZ)₂; and the like. Examples other thanthe metal complexes are PBD, OXD-7, TAZ, BPhen, BCP, and the like. Thesubstances described here are mainly substances having an electronmobility of 10⁻⁶ cm²/Vs or more. Note that other than the abovesubstances, any organic compound that has a property of transportingmore electrons than holes may be used.

Examples of the electron donor that can be used are alkali metals,alkaline-earth metals, rare-earth metals, metals that belong to Group 13in the periodic table and oxides or carbonates thereof, and preferablyspecifically lithium, cesium, magnesium, calcium, ytterbium, indium,lithium oxide, cesium carbonate, and the like. An organic compound suchas tetrathianaphthacene may be used as the electron donor.

By forming the charge generation layer 313 with any of the abovematerials, it is possible to suppress an increase in drive voltagecaused when the EL layers are stacked.

Although the light-emitting element having two light-emitting units isdescribed in this embodiment, the embodiment can be applied to alight-emitting element in which three or more light-emitting units arestacked as illustrated in FIG. 2B. For example, in a stack structurehaving n layers (n is a natural number greater than or equal to 2), thecharge generation layer 313 is interposed between an m-th light-emittingunit and an (m+1)-th light-emitting unit en is a natural number greaterthan or equal to 1 and less than or equal to (n−1)). When a plurality oflight-emitting units with a charge generation layer interposedtherebetween are arranged between a pair of electrodes, as in thelight-emitting element of this embodiment, it is possible to realize anelement having a long lifetime which can emit light with a highluminance while current density is kept low.

Furthermore, by making emission colors of the light-emitting unitsdifferent, light having a desired color can be obtained from thelight-emitting element as a whole. For example, the emission colors offirst and second light-emitting units are complementary in alight-emitting element having the two light-emitting units, whereby thelight-emitting element can be made to emit white light as a whole. Notethat the term “complementary” means color relationship in which anachromatic color is obtained when colors are mixed. That is, emission ofwhite light can be obtained by mixture of light emitted from substanceswhose emission colors are complementary colors. Further, the same can beapplied to a light-emitting element having three light-emitting units.For example, the light-emitting element as a whole can emit white lightwhen the emission color of the first light-emitting unit is red, theemission color of the second light-emitting unit is green, and theemission color of the third light-emitting unit is blue.

Note that this embodiment can be combined with any of the otherembodiments as appropriate.

(Embodiment 4)

In Embodiment 4, a light-emitting device having a light-emitting elementof one embodiment of the present invention will be described withreference to FIGS. 3A and 3B. Note that FIG. 3A is a top viewillustrating the light-emitting device, and FIG. 3B is a cross-sectionalview taken along lines A-B and C-D of FIG. 3A.

In FIG. 3A, reference numeral 401 denotes a driver circuit portion (asource driver circuit), reference numeral 402 denotes a pixel portion,and reference numeral 403 denotes a driver circuit portion (a gatedriver circuit), which are each indicated by dotted lines. Referencenumeral 404 denotes a sealing substrate, reference numeral 405 denotes asealant, and a portion enclosed by the sealing material 405 is a space407.

Note that a lead wiring 408 is a wiring for transmitting signals thatare to be inputted to the source driver circuit 401 and the gate drivercircuit 403, and receives a video signal, a clock signal, a startsignal, a reset signal, and the like from an FPC 409 which serves as anexternal input terminal. Although only the FPC is illustrated here, aprinted wiring board (PWB) may be attached to the FPC. Thelight-emitting device in this specification includes not only alight-emitting device itself but also a light-emitting device to whichan FPC or a PWB is attached.

Next, a cross-sectional structure will be described with reference toFIG. 3R The driver circuit portion and the pixel portion are formed overan element substrate 410. Here, the source driver circuit 401 which isthe driver circuit portion and one pixel in the pixel portion 402 areillustrated.

Note that as the source driver circuit 401, a CMOS circuit whichincludes an n-channel TFT 423 and a p-channel TFT 424 is formed. Thedriver circuit may be any of a variety of circuits formed with TFTs,such as a CMOS circuit, a PMOS circuit, or an NMOS circuit. Although adriver-integrated type in which a driver circuit is formed over thesubstrate is described in this embodiment, the present invention is notlimited to this type, and the driver circuit can be formed outside thesubstrate.

The pixel portion 402 includes a plurality of pixels having a switchingTFT 411, a current control TFT 412, and a first electrode 413electrically connected to a drain of the current control TFT 412. Notethat an insulator 414 is formed to cover an end portion of the firstelectrode 413. Here, the insulator 414 is formed by using a positivetype photosensitive acrylic resin film.

In order to improve coverage, the insulator 414 is provided such thateither an upper end portion or a lower end portion of the insulator 414has a curved surface with a curvature. For example, when positivephotosensitive acrylic resin is used as a material for the insulator414, it is preferable that only an upper end portion of the insulator414 have a curved surface with a radius of curvature (0.2 μm to 3 μm).For the insulator 414, it is also possible to use either a negative typethat becomes insoluble in an etchant by light irradiation or a positivetype that becomes soluble in an etchant by light irradiation.

A light-emitting layer 416 and a second electrode 417 are formed overthe first electrode 413. Here, as a material for forming the firstelectrode 413 functioning as the anode, a material having a high workfunction is preferably used. For example, it is possible to use a singlelayer of an ITO film, an indium tin oxide film that includes silicon, anindium oxide film that includes 2 wt % to 20 wt % of zinc oxide, atitanium nitride film, a chromium film, a tungsten film, a Zn film, a Ptfilm, or the like, a stacked layer of a titanium nitride film and a filmthat mainly includes aluminum, a three-layer structure of a titaniumnitride film, a film that mainly includes aluminum and a titaniumnitride film, or the like. Note that, when a stacked layer structure isemployed, resistance of a wiring is low and a favorable ohmic contact isobtained.

In addition, the light-emitting layer 416 is formed by any of variousmethods such as an evaporation method using an evaporation mask, adroplet discharging method like an inkjet method, a printing method, anda spin coating method. The light-emitting layer 416 includes a triazolederivative described in Embodiment 1. Further, another material includedin the light-emitting layer 416 may be a low molecular material, anoligomer, a dendrimer, a high molecular material, or the like.

As a material used for the second electrode 417 which is formed over thelight-emitting layer 416 and serves as a cathode, it is preferable touse a material having a low work function (e.g., Al, Mg, Li, Ca, or analloy or a compound thereof such as Mg—Ag, Mg—In, Al—Li, LiF, or CaF₂).In order that light generated in the light-emitting layer 416 betransmitted through the second electrode 417, a stack of a metal thinfilm having a reduced thickness and a transparent conductive film (e.g.,ITO, indium oxide containing 2 wt % to 20 wt % of zinc oxide, indiumoxide-tin oxide that includes silicon or silicon oxide, or zinc oxide(ZnO)) is preferably used for the second electrode 417.

Further, the sealing substrate 404 is attached to the element substrate410 with the sealing material 405 whereby, a light-emitting element 418is provided in the space 407 enclosed by the element substrate 410, thesealing substrate 404, and the sealing material 405. The space 407 maybe filled with an inert gas (such as nitrogen or argon), or the sealingmaterial 405.

Note that an epoxy-based resin is preferably used as the sealingmaterial 405. Such a material preferably allows as little moisture andoxygen as possible to penetrate. As a material used for the sealingsubstrate 404, a plastic substrate formed of FRP (fiberglass-reinforcedplastics), PVF (polyvinyl fluoride), polyester, acrylic, or the like canbe used other than a glass substrate or a quartz substrate.

As described above, the active matrix light-emitting device having thelight-emitting element of one embodiment of the present invention can beobtained.

Further, a light-emitting element of one embodiment of the presentinvention can be used for a passive matrix light-emitting device as wellas the above active matrix light-emitting device. FIGS. 4A and 4Billustrate a perspective view and a cross-sectional view of a passivematrix light-emitting device using a light-emitting element of oneembodiment of the present invention. Note that FIG. 4A is a perspectiveview of the light-emitting device, and FIG. 4B is a cross-sectional viewtaken along line X-Y of FIG. 4A.

In FIGS. 4A and 4B, an EL layer 504 is provided between a firstelectrode 502 and a second electrode 503 over a substrate 501. An endportion of the first electrode 502 is covered with an insulating layer505. In addition, a partition layer 506 is provided over the insulatinglayer 505. The sidewalls of the partition layer 506 are aslope so that adistance between both the sidewalls is gradually narrowed toward thesurface of the substrate. In other words, a cross section taken alongthe direction of the short side of the partition layer 506 istrapezoidal, and the base (side facing in a direction parallel to theplane direction of the insulating layer 505 and being in contact withthe insulating layer 505) is shorter than the upper side (side facing inthe direction parallel to the plane direction of the insulating layer505 and not being in contact with the insulating layer 505). Byproviding of the partition layer 506 in such a manner, a defect of alight-emitting element due to static electricity or the like can beprevented.

Thus, the passive matrix light-emitting device having a light-emittingelement of one embodiment of the present invention can be obtained.

The light-emitting devices described in Embodiment 4 (the active matrixlight-emitting device and the passive matrix light-emitting device) areboth formed using a light-emitting element of one embodiment of thepresent invention, and accordingly, the light-emitting devices have lowpower consumption.

Note that this embodiment can be combined with any other embodiment asappropriate.

(Embodiment 5)

In Embodiment 5, with reference to FIGS. 5A to 5E and FIG. 6,description is given of examples of a variety of electronic devices andlighting devices that are completed by using a light-emitting devicewhich is one embodiment of the present invention.

Examples of the electronic devices to which the light-emitting device isapplied are television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, cameras such as digitalcameras and digital video cameras, digital photo frames, cellular phones(also referred to as portable telephone devices), portable gamemachines, portable information terminals, audio playback devices, largegame machines such as pin-ball machines, and the like. Specific examplesof these electronic devices and a lighting device are illustrated inFIGS. 5A to 5E.

FIG. 5A illustrates an example of a television device. In the televisiondevice 7100, a display portion 7103 is incorporated into a housing 7101.The display portion 7103 is capable of displaying images, and thelight-emitting device can be used for the display portion 7103. Inaddition, here, the housing 7101 is supported by a stand 7105.

The television device 7100 can be operated by an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote controller 7110 may be provided witha display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the receiver, general television broadcastingcan be received. Furthermore, when the television device 7100 isconnected to a communication network by wired or wireless connection viathe modem, one-way (from a transmitter to a receiver) or two-way(between a transmitter and a receiver, between receivers, or the like)data communication can be performed.

FIG. 5B illustrates a computer having a main body 7201, a housing 7202,a display portion 7203, a keyboard 7204, an external connecting port7205, a pointing device 7206, and the like. This computer ismanufactured by using a light-emitting device for the display portion7203.

FIG. 5C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be opened or folded.A display portion 7304 is incorporated into the housing 7301 and adisplay portion 7305 is incorporated into the housing 7302. In addition,the portable game machine illustrated in FIG. 5C includes a speakerportion 7306, a recording medium insertion portion 7307, an LED lamp7308, an input means (an operation key 7309, a connection terminal 7310,a sensor 7311 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), or a microphone 7312), and thelike. It is needless to say that the structure of the portable gamesmachine is not limited to the above as long as a light-emitting devicecan be used for at least either the display portion 7304 or the displayportion 7305, or both, and may include other accessories as appropriate.The portable game machine illustrated in FIG. 5C has a function ofreading out a program or data stored in a storage medium to display iton the display portion, and a function of sharing information withanother portable game machine by wireless communication. The portablegame machine illustrated in FIG. 5C can have a variety of functionswithout limitation to the above.

FIG. 5D illustrates an example of a cellular phone. The cellular phone7400 is provided with operation buttons 7403, an external connectionport 7404, a speaker 7405, a microphone 7406, and the like, in additionto a display portion 7402 incorporated into a housing 7401. Note thatthe cellular phone 7400 is manufactured using a light-emitting devicefor the display portion 7402.

When the display portion 7402 of the cellular phone 7400 illustrated inFIG. 5D is touched with a finger or the like, data can be input into thecellular phone 7400. Further, operations such as making a call andcreating e-mail can be performed by touch on the display portion 7402with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting information such ascharacters. The third mode is a display-and-input mode in which twomodes of the display mode and the input mode are mixed.

For example, in the case of making a call or creating e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on a screen can be inputted. In this case,it is preferable to display a keyboard or number buttons on almost theentire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside thecellular phone 7400, display on the screen of the display portion 7402can be automatically changed by determining the orientation of thecellular phone 7400 (whether the cellular phone is placed horizontallyor vertically for a landscape mode or a portrait mode).

The screen modes are switched by touch on the display portion 7402 oroperation with the operation buttons 7403 of the housing 7401.Alternatively, the screen modes can be switched depending on kinds ofimages displayed on the display portion 7402. For example, when a signalfor an image displayed on the display portion is data of moving images,the screen mode is switched to the display mode. When the signal is textdata, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed during a certain period, thescreen mode may be controlled so as to be switched from the input modeto the display mode.

The display portion 7402 can function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. Furthermore, by provision of abacklight or a sensing light source emitting a near-infrared light forthe display portion, an image of a finger vein, a palm vein, or the likecan also be taken.

FIG. 5E illustrates a desk lamp including a lighting portion 7501, ashade 7502, an adjustable atm 7503, a support 7504, a base 7505, and apower supply 7506. The desk lamp is manufactured using a light-emittingdevice for the lighting portion 7501. Note that the “lighting device”also encompasses ceiling lights, wall lights, and the like.

FIG. 6 illustrates an example in which a light-emitting device is usedfor an interior lighting device 801. Since the light-emitting device canhave a larger area, it can be used as a lighting device having a largearea. Furthermore, the light-emitting device can be used as a roll-typelighting device 802. As illustrated in FIG. 6, a desk lamp 803 describedwith reference to FIG. 5E may be used together in a room provided withthe interior lighting device 801.

In the above-described manner, electronic devices or lighting devicescan be obtained by application of a light-emitting device. Applicationrange of the light-emitting device is so wide that the light-emittingdevice can be applied to electronic devices in a variety of fields.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 4 asappropriate.

EXAMPLE 1 Synthesis Example 1

This example gives descriptions of a method of synthesizing3-[4-(dibenzothiophen-4-yl)phenyl)]-4,5-diphenyl-4H-1,2,4-triazole(abbreviation: DBTTAZ-II) represented by Structural Formula (100) above.

A scheme for the synthesis of DBTTAZ-II is illustrated in (C-1).

Into a 300-mL three neck flask were placed 1.9 g (5.3 mmol) of3-(4-bromophenyl)-4,5-diphenyl-4H-1,2,4-triazole, 1.3 g (5.8 mmol) ofdibenzothiophene-4-boronic acid, 0.17 g (0.56 mmol) oftri(ortho-tolyl)phosphine, 50 mL of ethylene glycol dimethyl ether, and5 mL of a 2M aqueous solution of potassium carbonate. This mixture wasdegassed by stirring under reduced pressure, and the air in the flaskwas replaced with nitrogen. To this mixture was added 29 mg (0.13 mmol)of palladium(II) acetate. This mixture was stirred under a nitrogenstream at 80° C. for 4 hours. After a predetermined time had elapsed,water was added to this mixture, and organic substances were extractedfrom the aqueous layer with toluene. The solution of the obtainedextract was combined with the organic layer, and the mixture was washedwith saturated brine and dried with magnesium sulfate. The obtainedmixture was gravity filtered, and the filtrate was concentrated to givea solid. The obtained solid was purified by silica gel columnchromatography. At this time, a mixed solvent (chloroform and ethylacetate in a 6:1 ratio) was used as a developing solvent. Furthermore,recrystallization from toluene was carried out, whereby 2.3 g of a whitepowder of the substance to be produced was obtained in 89% yield.

By a train sublimation method, 2.3 g of the obtained white powder of thesubstance to be produced was purified. In the purification, the whitepowder was heated at 250° C. under a pressure of 10 Pa with a flow rateof argon gas of 5 mL/min. After the purification, 1.5 g of a whitepowder was recovered in 65% yield.

A nuclear magnetic resonance (NMR) method identified this compound as3-[4-(dibenzothiophen-4-yl)phenyl)]-4,5-diphenyl-4H-1,2,4-triazole(abbreviation: DBTTAZ-II), which was the substance to be produced.

¹H NMR data of the obtained compound are as follows: ¹H NMR (DMSO-d₆,300 MHz): δ (ppm)=7.34-7.45 (m, 5H), 7.52-7.66 (m, 11H), 7.76 (d, J=8.4Hz, 2H), 8.02-8.04 (m, 1H), 8.41-8.43 (m, 2H).

FIGS. 7A and 7B show the ¹H NMR charts. Note that FIG. 7B is a chartshowing an enlarged part of FIG. 7A in the range of 7.0 ppm to 9.0 ppm.

Further, FIG. 8A shows an absorption spectrum of a toluene solution ofDBTTAZ-II, and FIG. 8B shows an emission spectrum thereof. FIG. 9A showsan absorption spectrum of a thin film of DBTTAZ-II, and FIG. 9B shows anemission spectrum thereof. An ultraviolet-visible spectrophotometer(V-550, manufactured by JASCO Corporation) was used for themeasurements. Samples were prepared in such a manner that the solutionwas put in a quartz cell and the thin film was obtained by evaporationonto a quartz substrate. The absorption spectrum of the solution wasobtained by subtracting the absorption spectra of quartz and toluenefrom those of quartz and the solution, and the absorption spectrum ofthe thin film was obtained by subtracting the absorption spectrum of aquartz substrate from those of the quartz substrate and the thin film.In FIG. 8A and FIG. 9A, the horizontal axis represents wavelength (nm)and the vertical axis represents absorption intensity (arbitrary unit).In FIG. 8B and FIG. 9B, the horizontal axis represents wavelength (nm)and the vertical axis represents emission intensity (arbitrary unit). Inthe case of the toluene solution, absorption peaks were at around 292nm, 305 nm, and 332 nm, and an emission wavelength peak was at 365 nm(at an excitation wavelength of 290 nm). In the case of the thin film,absorption peaks were at around 269 nm, 294 nm, and 338 nm, and anemission wavelength peak was at 391 nm (at an excitation wavelength of341 nm).

EXAMPLE 2

In this example, a light-emitting element according to one embodiment ofthe present invention will be described with reference to FIG. 10A.Structural formulae of materials used in this example are illustratedbelow.

Hereinafter, methods of fabricating Light-emitting Element 1 of thisexample and Reference Light-emitting Element 2 will be described.

(Light-Emitting Element 1)

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 1100 by a sputtering method, whereby a firstelectrode 1101 was formed. Note that its thickness was set to 110 nm andthe electrode area was set to 2 mm×2 mm.

Next, as pretreatment for forming the light-emitting element on thesubstrate 1100, after washing of a surface of the substrate with waterand baking that was performed at 200° C. for one hour, UV ozonetreatment was performed for 370 seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate 1100was cooled down for about 30 minutes.

Next, the substrate 1100 provided with the first electrode 1101 wasfixed to a substrate holder in a vacuum evaporation apparatus so that asurface on which the first electrode 1101 was provided faced downward.The pressure in the vacuum evaporation apparatus was reduced to about10⁻⁴ Pa. Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP) and molybdenum(VI) oxide were co-evaporated toform a hole-injection layer 1111 on the first electrode 1101. Thethickness of the hole-injection layer 1111 was set to 50 nm, and theweight ratio of BPAFLP to molybdenum(VI) oxide was adjusted to 4:2(=BPAFLP:molybdenum oxide). Note that the co-evaporation method refersto an evaporation method in which evaporation is carried out from aplurality of evaporation sources at the same time in one treatmentchamber.

Next, a BPAFLP film was formed to a thickness of 10 nm on thehole-injection layer 1111, whereby a hole-transport layer 1112 wasformed.

Further,3-[4-(dibenzothiophen-4-yl)phenyl)]-4,5-diphenyl-4H-1,2,4-triazole(abbreviation: DBTTAZ-II) synthesized in Example 1,4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), and tris(2-phenylpyridinato-N,C^(2′))iridium(III)(abbreviation: Ir(ppy)₃) were co-evaporated to form a firstlight-emitting layer 1113 a on the hole-transport layer 1112. The weightratio of DBTTAZ-II to PCBA1BP and Ir(ppy)₃ was adjusted to 1:0.2:0.08(=DBTTAZ-II:PCBA1BP:Ir(ppy)₃). The thickness of the first light-emittinglayer 1113 a was set to 20 nm.

Next, DBTTAZ-II and Ir(ppy)₃ were co-evaporated, whereby a secondlight-emitting layer 1113 b was formed on the first light-emitting layer1113 a. The weight ratio of DBTTAZ-II to Ir(ppy)₃ was adjusted to 1:0.08(=DBTTAZ-II:Ir(ppy)₃). The thickness of the second light-emitting layer1113 b was set to 20 nm.

Further, a DBTTAZ-II film was formed to a thickness of 15 nm on thesecond light-emitting layer 1113 b, whereby a first electron-transportlayer 1114 a was formed.

Then, a bathophenanthroline (abbreviation: BPhen) film was formed to athickness of 15 nm on the first electron-transport layer 1114 a, wherebya second electron-transport layer 1114 b was formed.

Further, a lithium fluoride (LiF) film was formed to a thickness of 1 nmon the second electron-transport layer 1114 b by evaporation, whereby anelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as a second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 1 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

(Reference Light-emitting Element 2)

Tto form the first light-emitting layer 1113 a of ReferenceLight-emitting Element 2,9-[4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl]-9H-carbazole(abbreviation: CzTAZ-I), PCBA1BP, and Ir(ppy)₃ were co-evaporated. Theweight ratio of CzTAZ-I to PCBA1BP and Ir(ppy)₃ was adjusted to1:0.25:0.08 (=CzTAZ-I:PCBA1BP:Ir(ppy)₃). The thickness of the firstlight-emitting layer 1113 a was set to 20 nm.

Furthermore, CzTAZ-I and Ir(ppy)₃ were co-evaporated to form the secondlight-emitting layer 1113 b of Reference Light-emitting Element 2. Theweight ratio of CzTAZ-I to Ir(ppy)₃ was adjusted to 1:0.08(=CzTAZ-I:Ir(ppy)₃). The thickness of the second light-emitting layer1113 b was set to 20 nm.

The first electron-transport layer 1114 a of Reference Light-emittingElement 2 was formed with a 15-nm-thick CzTAZ-I film. The componentsother than the first light-emitting layer 1113 a, the secondlight-emitting layer 1113 b, and the first electron-transport layer 1114a were formed in the same manner as those of Light-emitting Element 1.

Table 1 shows element structures of Light-emitting Element 1 andReference Light-emitting Element 2 obtained as described above.

TABLE 1 first second first second hole- hole- light- light- electron-electron- electron- first injection transport emitting emittingtransport transport injection second electrode layer layer layer layerlayer layer layer electrode Light- ITSO BPAFLP:MoOx BPAFLP DBTTAZ-DBTTAZ- DBTTAZ-II BPhen LiF Al emitting 110 nm (=4:2) 10 nmII:PCBA1BP:Ir(ppy)₃ II:Ir(ppy)₃ 15 nm 15 nm 1 nm 200 nm Element 1 50 nm(=1:0.2:0.08) (=1:0.08) 20 nm 20 nm Reference ITSO BPAFLP:MoOx BPAFLPCzTAZ- CzTAZ- CzTAZ-I BPhen LiF Al Light- 110 nm (=4:2) 10 nmI:PCBA1BP:Ir(ppy)₃ I:Ir(ppy)₃ 15 nm 15 nm 1 nm 200 nm emitting 50 nm(=01:0.25:0.08) (=1:0.08) Element 2 20 nm 20 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element1 and Reference Light-emitting Element 2 were sealed so as not to beexposed to air. Then, operation characteristics of these elements weremeasured. Note that the measurements were carried out at roomtemperature (in the atmosphere kept at 25° C.).

FIG. 11 shows the current density versus luminance characteristics ofLight-emitting Element 1 and Reference Light-emitting Element 2. In FIG.11, the horizontal axis represents current density (mA/cm²) and thevertical axis represents luminance (cd/m²). In addition, FIG. 12 showsthe voltage versus luminance characteristics. In FIG. 12, the horizontalaxis represents voltage (V) and the vertical axis represents luminance(cd/m²). FIG. 13 shows the luminance versus current efficiencycharacteristics. In FIG. 13, the horizontal axis represents luminance(cd/m²) and the vertical axis represents current efficiency (cd/A). FIG.14 shows the voltage versus current characteristics. In FIG. 14, thehorizontal axis represents voltage (V) and the vertical axis representscurrent (mA). Further, Table 2 shows the voltage (V), current density(mA/cm²), CIE chromaticity coordinates (x, y), current efficiency(cd/A), and external quantum efficiency (%) of the light-emittingelement at a luminance of around 1000 cd/m².

TABLE 2 CIE chromaticity current coordinates x current external voltagedensity CIE chromaticity luminance efficiency quantum (V) (mA/cm²)coordinates y (cd/m²) (cd/A) efficiency (%) Light-emitting 3.4 1.8 0.320.62 1100 62 18 Element 1 Reference Light- 5.2 2.0 0.32 0.61 1000 52 16emitting Element 2

As shown in Table 2, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 1 were (0.32, 0.62) at a luminance of 1100 cd/m²,and those of Reference Light-emitting Element 2 were (0.32, 0.61) at aluminance of 1000 cd/m². It was found that these light-emitting elementsexhibited light emission from Ir(ppy)₃.

To produce a certain luminance, a lower voltage was used inLight-emitting Element 1 than in Reference Light-emitting Element 2, ascan be seen from FIG. 12. This is because Light-emitting Element 1 canobtain a larger amount of current at a lower voltage. Therefore, it canbe said that Light-emitting Element 1 is an element capable of drivingat a lower voltage than Reference Light-emitting Element 2.

In addition, Light-emitting Element 1 has a higher current efficiencythan Reference Light-emitting Element 2, as shown in FIG. 13 and Table2.

As described above, the light-emitting element having high currentefficiency and the capability of low-voltage driving was able to befabricated using DBTTAZ-II, which was produced in Example 1, as the hostmaterial of a light-emitting layer.

Next, Light-emitting Element 1 and Reference Light-emitting Element 2were subjected to reliability tests. Results of the reliability testsare shown in FIG. 15. In FIG. 15, the vertical axis representsnormalized luminance (%) with an initial luminance of 100%, and thehorizontal axis represents driving time (h) of the elements. In thereliability tests, Light-emitting Element 1 of this example andReference Light-emitting Element 2 were driven under the conditionswhere the initial luminance was 1000 cd/m² and the current density wasconstant. As can be seen from FIG. 15, Light-emitting Element 1 kept 50%of the initial luminance until after 440 hours had elapsed, butLight-emitting Element 2 kept 50% of the initial luminance until after14 hours had elapsed. These results of the reliability tests revealedthat Light-emitting Element 1, to which one embodiment of the presentinvention was applied, had a longer lifetime than ReferenceLight-emitting Element 2, in which CzTAZ-I, a substance havingsubstantially as high triplet excitation energy as a triazole derivativeof one embodiment of the present invention, was used as the hostmaterial of the light-emitting layer.

EXAMPLE 3

In this example, a light-emitting element according to one embodiment ofthe present invention will be described with reference to FIG. 10B.Structural formulae of materials used in this example are illustratedbelow. Note that the formulae of the materials which are described abovewill be omitted.

Hereinafter, methods of fabricating Light-emitting Element 3 of thisexample will be described.

(Light-Emitting Element 3)

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 1100 by a sputtering method, whereby a firstelectrode 1101 was formed. Note that its thickness was set to 110 nm andthe electrode area was set to 2 mm×2 mm.

Next, as pretreatment for forming the light-emitting element on thesubstrate 1100, after washing of a surface of the substrate with waterand baking that was performed at 200° C. for one hour, UV ozonetreatment was performed for 370 seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate 1100was cooled down for about 30 minutes.

Next, the substrate 1100 provided with the first electrode 1101 wasfixed to a substrate holder in a vacuum evaporation apparatus so that asurface on which the first electrode 1101 was provided faced downward.The pressure in the vacuum evaporation apparatus was reduced to about10⁻⁴ Pa. Then, 4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation:TCTA) and molybdenum(VI) oxide were co-evaporated to form ahole-injection layer 1111 on the first electrode 1101. The thickness ofthe hole-injection layer 1111 was set to 50 nm, and the weight ratio ofTCTA to molybdenum(VI) oxide was adjusted to 4:2 (=TCTA:molybdenumoxide). Note that the co-evaporation method refers to an evaporationmethod in which evaporation is carried out from a plurality ofevaporation sources at the same time in one treatment chamber.

Next, a TCTA film was formed to a thickness of 10 nm on thehole-injection layer 1111, whereby a hole-transport layer 1112 wasformed.

Further, DBTTAZ-II synthesized in Example 1, TCTA, andbis[2-(4,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(abbreviation: Fir(pic), FIrpic) were co-evaporated to form alight-emitting layer 1113 on the hole-transport layer 1112. The weightratio of DBTTAZ-II to TCTA and FIrpic was adjusted to 1:0.15:0.06(=DBTTAZ-II:TCTA:FIrpic). The thickness of the light-emitting layer 1113was set to 30 nm.

Further, a DBTTAZ-II film was formed to a thickness of 10 nm on thelight-emitting layer 1113, whereby a first electron-transport layer 1114a was formed.

Then, a bathophenanthroline (abbreviation: BPhen) film was formed to athickness of 20 nm on the first electron-transport layer 1114 a, wherebya second electron-transport layer 1114 b was formed.

Further, a lithium fluoride (LiF) film was formed to a thickness of 1 nmon the second electron-transport layer 1114 b by evaporation, whereby anelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as a second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 3 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 3 shows an element structure of Light-emitting Element 3 obtainedas described above.

TABLE 3 hole- hole- light first second electron- first injectiontransport emitting- electron- electron- injection second electrode layerlayer layer transport layer transport layer layer electrode Light- ITSOTCTA:MoOx TCTA DBTTAZ-II:TCTA:Flrpio DBTTAZ-II BPhen LiF Al emitting 110nm (=4:2) 10 nm (=1:0.15:0.06) 10 nm 20 nm 1 nm 200 nm Element 3 50 nm30 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element3 is sealed so as not to be exposed to air. Then, operationcharacteristics of this element were measured. Note that themeasurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 16 shows the current density versus luminance characteristics ofLight-emitting Element 3. In FIG. 16, the horizontal axis representscurrent density (mA/cm²) and the vertical axis represents luminance(cd/m²). In addition, FIG. 17 shows the voltage versus luminancecharacteristics. In FIG. 17, the horizontal axis represents voltage (V)and the vertical axis represents luminance (cd/m²). FIG. 18 shows theluminance versus current efficiency characteristics. In FIG. 18, thehorizontal axis represents luminance (cd/m²) and the vertical axisrepresents current efficiency (cd/A). FIG. 19 shows the voltage versuscurrent characteristics. In FIG. 19, the horizontal axis representsvoltage (V) and the vertical axis represents current (mA). Further,Table 4 shows the voltage (V), current density (mA/cm²), CIEchromaticity coordinates (x, y), current efficiency (cd/A), and externalquantum efficiency (%) of the light-emitting element at a luminance ofaround 1000 cd/m².

TABLE 4 CIE chromaticity current coordinates x current external densityCIE chromaticity luminance efficiency quantum voltage (V) (mA/cm²)coordinates y (cd/m²) (cd/A) efficiency (%) Light- 5.8 26 0.21 0.40 10003.9 1.7 emitting Element 3

As shown in Table 4, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 3 were (0.21, 0.40) at a luminance of 1000 cd/m².It was revealed that this light-emitting element exhibited lightemission from FIrpic. The light emission from FIrpic, which producesblue light emission at short wavelengths, was formed to show highefficiency since a triazole derivative having high triplet excitationenergy was used in the light-emitting element of this example. It wasdemonstrated that application of the present invention enabled efficientlight emission from FIrpic, a phosphorescent compound that producesshort-wavelength light emission.

EXAMPLE 4 Synthesis Example 2

This example gives descriptions of a method of synthesizing4-[4-(dibenzothiophen-4-yl)phenyl)]-3,5-diphenyl-4H-1,2,4-triazole(abbreviation: 4DBTTAZ-II) represented by Structural Formula (150)above.

A scheme for the synthesis of 4DBTTAZ-II is illustrated in (D−1).

Into a 100-mL three neck flask were placed 1.1 g (3.0 mmol) of4-(4-bromophenyl)-3,5-diphenyl-4H-1,2,4-triazole, 0.74 g (3.2 mmol) ofdibenzothiophene-4-boronic acid, and 0.21 g (0.68 mmol) oftris(2-methylphenyl)phosphine, and the air in the flask was replacedwith nitrogen. Into this flask were placed 30 mL of toluene, 3.0 mL ofethanol, and 3.0 mL of a 2M aqueous solution of potassium carbonate.This mixture was degassed by stirring under reduced pressure. To thismixture was added 51 mg (0.23 mmol) of palladium(II) acetate. Thismixture was stirred under a nitrogen stream at 80° C. for 11 hours.Furthermore, to the mixture were added 3.0 mL of a 2M aqueous solutionof potassium carbonate, 0.14 g (0.46 mmol) oftris(2-methylphenyl)phosphine, and 21 mg (93 μmol) of palladium(II)acetate, and the mixture was stirred at 100° C. for 8 hours. After that,water was added to this mixture, and organic substances were extractedfrom the aqueous layer of this mixture with chloroform. The solution ofthe obtained extract was combined with the organic layer, and themixture was washed with saturated brine and dried with magnesiumsulfate. The obtained mixture was gravity filtered, and the filtrate wasconcentrated to give a solid. The obtained solid was purified by silicagel column chromatography (with a developing solvent of toluene andethyl acetate in a 4:1 ratio). Furthermore, recrystallization fromtoluene was carried out, whereby 1.1 g of a white powder of thesubstance to be produced was obtained in 76% yield.

By a train sublimation method, 1.1 g of the white powder of thesubstance to be produced was purified. In the purification, the whitepowder was heated at 250° C. under a pressure of 2.7 Pa with a flow rateof argon gas of 5 mL/min After the purification, 0.91 g of a whitepowder was recovered in 81% yield.

A nuclear magnetic resonance (NMR) method identified this compound as4-[4-(dibenzothiophen-4-yl)phenyl)]-3,5-diphenyl-4H-1,2,4-triazole(abbreviation: 4DBTTAZ-II), which was the substance to be produced.

¹H NMR data of the obtained compound are as follows: ¹H NMR (CDCl3, 300MHz): δ (ppm)=7.29 (d, J=8.4 Hz, 2H), 7.33-7.44 (m, 6H), 7.49-7.53 (m,7H), 7.59 (t, J=7.8 Hz, 1H), 7.80 (d, J=8.7 Hz, 2H), 7.85-7.88 (m, 1H),8.20-8.22 (m, 2H).

FIGS. 20A and 20B show the ¹H NMR charts. Note that FIG. 20B is a chartshowing an enlarged part of FIG. 20A in the range of 7.0 ppm to 8.5 ppm.

Further, FIG. 21A shows an absorption spectrum of a toluene solution of4DBTTAZ-II, and FIG. 21B shows an emission spectrum thereof. Anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements. The solution was put in aquartz cell to prepare a sample. The absorption spectrum of the solutionwas obtained by subtracting the absorption spectra of quartz and toluenefrom those of quartz and the solution. In FIG. 21A, the horizontal axisrepresents wavelength (nm) and the vertical axis represents absorptionintensity (arbitrary unit). In FIG. 21B, the horizontal axis representswavelength (nm) and the vertical axis represents emission intensity(arbitrary unit). With the toluene solution, absorption peaks were ataround 282 nm and 332 nm, and an emission wavelength peak was at 360 nm(at an excitation wavelength of 334 nm).

(Reference Example 1)

A method of synthesizing4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)used in the above Examples will be specifically described. A structureof BPAFLP is illustrated below.

[Step 1: Method of Synthesizing 9-(4-Bromophenyl)-9-phenylfluorene]

In a 100-mL three-neck flask, 1.2 g (50 mmol) of magnesium was heatedand stirred under reduced pressure for 30 minutes, and was activated.The magnesium was cooled to room temperature, and a nitrogen atmospherewas formed. Then, several drops of dibromoethane were added, so thatfoam formation and heat generation were confirmed. After 12 g (50 mmol)of 2-bromobiphenyl dissolved in 10 mL of diethyl ether was slowlydripped into this mixture, the mixture was heated and stirred underreflux for 2.5 hours, whereby a Grignard reagent was prepared.

Into a 500-mL three-neck flask were placed 10 g (40 mmol) of4-bromobenzophenone and 100 mL of diethyl ether. After the Grignardreagent which was synthesized in advance was slowly dripped into thismixture, the mixture was heated and stirred under reflux for 9 hours

After reaction, this mixture solution was filtered to give a residue.The obtained residue was dissolved in 150 mL of ethyl acetate, and1N-hydrochloric acid was added to the mixture until it was made acid,which was then stirred for 2 hours. The organic layer of this liquid waswashed sequentially with water, and magnesium sulfate was added theretoto remove moisture. This suspension was filtered, and the obtainedfiltrate was concentrated to give an oily substance.

Into a 500-mL recovery flask were placed this oily substance, 50 mL ofglacial acetic acid, and 1.0 mL of hydrochloric acid. The mixture wasstirred and heated at 130° C. for 1.5 hours under a nitrogen atmosphereto be reacted.

After the reaction, this reaction mixture solution was filtrated to givea residue. The obtained residue was washed sequentially with water, anaqueous sodium hydroxide solution, water, and methanol in this order.Then, the mixture was dried to give 11 g of a white powder in 69% yield,which is the substance to be produced. A reaction scheme of the abovesynthesis method is illustrated in the following (E−1).

[Step 2: Method of Synthesizing4-Phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)]

Into a 100-mL three-neck flask were placed 3.2 g (8.0 mmol) of9-(4-bromophenyl)-9-phenylfluorene, 2.0 g (8.0 mmol) of4-phenyl-diphenylamine, 1.0 g (10 mmol) of sodium tert-butoxide, and 23mg (0.04 mmol) of bis(dibenzylideneacetone)palladium(0), and the air inthe flask was replaced with nitrogen. Then, 20 mL of dehydrated xylenewas added to this mixture. After the mixture was degassed by stirringunder reduced pressure, 0.2 mL (0.1 mmol) of tri(tert-butyl)phosphine (a10 wt % hexane solution) was added to the mixture. This mixture wasstirred and heated at 110° C. for 2 hours under a nitrogen atmosphere,and was reacted.

After the reaction, 200 mL of toluene was added to this reaction mixturesolution, and this suspension was filtrated through Florisil (producedby Wako Pure Chemical Industries, Ltd., Catalog No. 540-00135) andCelite (produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855). The obtained filtrate was concentrated, and the resultingsubstance was purified by silica gel column chromatography (with adeveloping solvent of toluene and hexane in a 1:4 ratio). The obtainedfractions were concentrated, and acetone and methanol were added to themixture. The mixture was irradiated with ultrasonic waves and thenrecrystallized to give 4.1 g of a white powder in 92% yield, which isthe substance to be produced. A reaction scheme of the above synthesismethod is illustrated in the following (E-2).

The Rf values of the substance to be produced,9-(4-bromophenyl)-9-phenylfluorene, and 4-phenyl-diphenylamine wererespectively 0.41, 0.51, and 0.27, which were found by silica gel thinlayer chromatography (TLC) (with a developing solvent of ethyl acetateand hexane in a 1:10 ratio).

The compound obtained by the above Step 2 was subjected to a nuclearmagnetic resonance (NMR) method. The measurement data are shown below.The measurement results indicate that the obtained compound was BPAFLP,which is a fluorene derivative.

¹H NMR (CDCl₃, 300 MHz): δ (ppm)=6.63-7.02 (m, 3H), 7.06-7.11 (m, 6H),7.19-7.45 (m, 18H), 7.53-7.55 (m, 2H), 7.75 (d, J=6.9, 2H).

This application is based on Japanese Patent Application serial no.2010-116997 filed with the Japan Patent Office on May 21, 2010, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting element comprising: a pair ofelectrodes; and a light-emitting layer between the pair of electrodes,the light-emitting layer comprising a first triazole derivative and alight-emitting substance, wherein the first triazole derivative isrepresented by General Formula (G1), wherein a substituent representedby General Formula (G2) is bonded to one of Ar¹ and Ar², and

wherein: A represents sulfur; the one of Ar¹ and Ar² represents asubstituted or unsubstituted arylene group having 6 to 13 carbon atoms;the other of Ar¹ and Ar², and Ar³ which are not bonded to thesubstituent separately represent a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms; and R¹ to R⁷ separately representhydrogen, an alkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.
 2. Thelight-emitting element according to claim 1, wherein the light-emittingsubstance comprises tris(2-phenylpyridinato-N,C^(2′))iridium(III). 3.The light-emitting element according to claim 1, wherein thelight-emitting substance emits phosphorescence and has an emission peakat a wavelength greater than or equal to 400 nm and less than or equalto 500 nm.
 4. The light-emitting element according to claim 1, furthercomprising an electron-transport layer, wherein the electron-transportlayer comprises a second triazole derivative, wherein the secondtriazole derivative is represented by General Formula (G1), wherein asubstituent represented by General Formula (G2) is bonded to one of Ar¹and Ar², and

wherein: A represents sulfur; the one of Ar¹ and Ar² represents asubstituted or unsubstituted arylene group having 6 to 13 carbon atoms;the other of Ar¹ and Ar², and Ar³ which are not bonded to thesubstituent separately represent a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms; and R¹ to R⁷ separately representhydrogen, an alkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.
 5. Alight-emitting device comprising the light-emitting element according toclaim
 1. 6. An electronic device comprising the light-emitting deviceaccording to claim
 5. 7. A lighting device comprising the light-emittingelement according to claim
 1. 8. A light-emitting element comprising: apair of electrodes; and a light-emitting layer between the pair ofelectrodes, the light-emitting layer comprising a first triazolederivative and a light-emitting substance, wherein the first triazolederivative is represented by General Formula (G1), wherein a substituentrepresented by General Formula (G2) is bonded to one of Ar¹ and Ar², and

wherein: A represents sulfur; the one of Ar¹ and Ar² represents asubstituted or unsubstituted phenylene group; the other of Ar¹ and Ar²,and Ar³ which are not bonded to the substituent separately represent asubstituted or unsubstituted phenyl group; and R¹ to R⁷ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms. 9.The light-emitting element according to claim 8, wherein thelight-emitting substance comprisestris(2-phenylpyridinato-N,C^(2′))iridium(III).
 10. The light-emittingelement according to claim 8, wherein the light-emitting substance emitsphosphorescence and has an emission peak at a wavelength greater than orequal to 400 nm and less than or equal to 500 nm.
 11. The light-emittingelement according to claim 8, further comprising an electron-transportlayer, wherein the electron-transport layer comprises a second triazolederivative, wherein the second triazole derivative is represented byGeneral Formula (G1), wherein a substituent represented by GeneralFormula (G2) is bonded to one of Ar¹ and Ar², and

wherein: A represents sulfur; the one of Ar¹ and Ar² represents asubstituted or unsubstituted phenylene group; the other of Ar¹ and Ar²,and Ar³ which are not bonded to the substituent separately represent asubstituted or unsubstituted phenyl group; and R¹ to R⁷ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms. 12.A light-emitting device comprising the light-emitting element accordingto claim
 8. 13. An electronic device comprising the light-emittingdevice according to claim
 12. 14. A lighting device comprising thelight-emitting element according to claim 8.